194 FIELD CoLuMBIAN MusEUM—GEOLOGY, VOL. I. 
detail. The portion which may sufficiently be designated as the shell, 
was found to be translucent chalcedony similar to that’ of the main 
mass, or what may be called the white, and for the most part con- 
fluent with it. It is, however, dark brown to black in color. On 
heating to redness this color disappeared, indicating organic matter 
to be the coloring ingredient. In one or two spots the shell was not 
homogeneous throughout, a thin white layer separating it from the 
main portion. This, on testing, proved to be carbonate of lime, indi- 
cating that here some of the original shell had not been replaced by the 
petrifying siliceous solutions. No definite structure or markings could 
be distinguished on the shell. While generally smooth in outline, under 
a lens it is seen to be rough and porous, owing doubtless to the action 
of the infiltrating waters. The original markings, if any, must have 
been destroyed by such an action. 
'The portion designated as representing the white of the egg is, 
as has been said, made up of pale gray translucent chalcedony. Itis 
homogeneous throughout except for occasional black blotches, some 
of which resemble in arrangement those of moss agate, while others 
show concentric distribution. It could not be determined without 
sacrificing too much of the specimen, whether these were formed by 
organic matter or by mineral matter such as oxides of iron or man- 
ganese. The chalcedony resembles in its characters that of the 
veins of that mineral which traverse the region and which have been 
described by other authors.* On heating fragments of the chal- 
cedony it turns white and opaque but yields only a trace of water. It 
is infusible and has a hardness of 7. 
It is to the portion designated as the yolk that the greatest inter- 
est attaches. This has already been described as a white opaque 
ovoid mass .66 inch in diameter, enveloped in the chalcedony. On 
close examination this white mass can be seen to be made up of two 
portions of about equal size which have different structure. That 
nearer the center of the egg is made up of little spherules and thin 
curving plates. The spherules average about 1 mm. in diameter and 
have a distinct concentric structure, coats of alternately opaque white 
and translucent dark matter being deposited around each center. So 
far as can be judged from the color of these coats they are opal and 
chalcedony, respectively, but color is not, of course, in such a case, 
an accurate criterion. The thin curving plates are similarly made up 
of white and dark layers. 
The other portion of the ‘‘yolk” is composed of a yellowish- 
*J. B. Hatcher, Am. Naturalist, March, 1893, p. st. Na Da eF Case, Am. Geologist, April, 1895, 
p. 248. 
